Request and Offer form
Request and Offer form is appropriate for any arms-length transaction where it might be important to review the contract later. This includes a social contract. Without this form, more social capital than necessary is at risk. The formality is an important form of hedging via etiquette - if things go wrong, they are restricted to only that one matter.
To put something in this form, state it as a Request. Anyone who wishes to respond will develop that request further into an Offer. If this is satisfactory, the request will be withdrawn and the offer accepted. If not, a Counter-Offer will be created but the original Request will remain visible for other competing Offers to respond to it. All of this should be recorded reliably. A legal contract almost always follows this format, for exactly the reason above: if things go wrong, issues are contained. They do not generally turn into a reputation war or something.
MoinMoin's Market Model (and all similar models like the stock market) rely on this form. It is probably the only real global standard.
One can look at wiki edits as following this form. An open link is a kind of request, and an attempt to create a viable page is an offer to close that link. If it is rejected, the page might be blanked or even deleted. A second offer can then be entertained, etc.. See also Unanimity Minus Two.